Analysis of water-soluble vitamins by micellar electrokinetic capillary chromatography

Seven water-soluble vitamins were determined simultaneously by micellar electrokinetic capillary chromatography with UV detection. All these compounds were separated from each other within ca. 22 min by using a carrier containing sodium dodecyl sulphate as the surfactant. On-column detection at 254 nm with ethyl p-aminobenzoate as the internal standard allowed sensitive, accurate and reproducible determination of these compounds. Five principal constituents of a vitamin injection were determined with relative standard deviations of less than 2.1%.     

Separation and measurement of desmosine and isodesmosine in vascular tissue hydrolysates by micellar electrokinetic capillary chromatography with a mixed micelle system

A micellar electrokinetic capillary chromatography (MEKC) method with a mixed micelle system for separation and measurement of desmosine (DES) and isodesmosine (IDES) in vascular tissue hydrolysates is described. The mixed micelle system was composed of a zwitterionic surfactant named 3-(N,N-dimethylhexadecylammonium)propanesulfonate (PAPS) and a nonionic surfactant polyethylene glycol dodecyl ether (Brij 35). By using 50 mM Tris-H(3)PO(4) (pH 2.5) containing 40 mM PAPS and 0.5% (m/v) Brij-35 as the optimal running buffer, DES and IDES were baseline separated from each other and from other hydrolyzed components of the vascular tissue. The limit of quantitation (LOQ) for DES and IDES were 3.00 x 10(-6)mol/L and 2.75 x 10(-6)mol/L, respectively. The relative standard deviation (RSD) of migration times and corrected peak area in terms of the inter-day and the intra-day repeatability were less than 1.7%. Hydrolysate samples of vascular tissues of rats were analyzed with the MEKC method with satisfied results.     

Analysis of clindamycin by micellar electrokinetic chromatography with a mixed micellar system.

This study details the development and validation of an optimized method with micellar electrokinetic chromatography for the analysis of clindamycin. The method uses a mixed micellar phase containing anionic sodium dodecylsulfate (SDS) and non ionic Brij 35 on an untreated fused-silica capillary. The influences of buffer concentration, pH, SDS, Brij 35 and organic modifier were investigated. Special attention was given to the role of the non ionic Brij 35 in the mixed micellar system. Optimization with a central composite design resulted in optimal separation conditions: background electrolyte containing 25 mM sodium tetraborate pH 7.75, 90 mM SDS, 14 mM Brij 35 and 21% acetonitrile. The applied voltage was 15 kV and the capillary temperature 15 degrees C. The method was robust and gave good linearity and repeatability. The limits of detection and quantitation were 0.05 and 0.15%, respectively, relative to a 2.5 mg/ml clindamycin solution. Two commercial bulk products were analysed with this system.     

Pesticide analysis by micellar electrokinetic capillary chromatography

On-capillary sample concentration using sample stacking for the improvement of detection limits for various pesticides separated by micellar electrokinetic capillary chromatography was examined. The dependence of the stacking on different parameters was investigated. An approximately 30-fold preconcentration was achieved by applying sample stacking. Employing a two-step enrichment process (solid-phase extraction combined with sample stacking), detection limits were improved and the sample volume for SPE was reduced. In addition, the total time for the analysis was considerably reduced. Detection limits were between 0.01 and 0.1 ng/ml under these enrichment conditions.     

Analysis of nucleic acid derivatives by micellar electrokinetic capillary chromatography

The use of micellar electrokinetic capillary chromatography (MECC) for the analysis of the major nucleobases, nucleosides, and nucleotides, and their chemically modified derivatives, has been developed and refined. The dimensions of the separating capillaries, the composition of the buffering systems, and the conditions used for electrophoresis were investigated in order to obtain the best performance. Particular emphasis was placed on the identification of the physiological constituents of nucleic acids and their chemically modified analogs: in vitro studies on calf thymus DNA exposed to genotoxic agents have demonstrated that adducted bases and nucleolides can be identified by MECC.     

Separation of coumarins by micellar electrokinetic capillary chromatography

Nine coumarins were successfully separated simultaneously using micellar electrokinetic capillary chromatography with 4-hydroxybenzoic acid as an internal standard. A carrier composed of buffer solution (20 mM sodium dodecyl sulfate-15 mM sodium borate-15 mM sodium dihydrogenphosphate)-acetonitrile (24:1) was found to be the most suitable electrolyte for this separation. The analysis time (22 min) was shorter than that using high-performance liquid chromatography (47 min). Contents of coumarins in the crude drug of Angelicae Tuhou Radix could be easily determined by the proposed method.     

Serum iohexol analysis by micellar electrokinetic capillary chromatography

A simple and rapid ( approximately 4 min) method for the measurement of iohexol in serum for assessing the glomerular filtration rate is described. It is based on direct serum injection on the capillary by MEKC. The method is linear between 8 and 260 mg/L, with an RSD of peak height of 2.9%. Several simple steps have contributed to an improved daily precision, such as choosing a high pH buffer, increasing the SDS concentration, frequent standardization, and eliminating any sample pretreatment.     

Optimization strategies in micellar electrokinetic capillary chromatography

Summary Computer-assisted procedures for the one-parameter optimization of the surfactant concentration and the concentration of urea or D-glucose as modifiers in micellar electrokinetic capillary chromatography have been developed. These procedures permit a rapid optimization of one parameter on the basis of only two experiments. Predicted values are compared to empirically obtained optimum values. The influence of the modifier concentration on the critical micelle concentration of sodium dodecyl sulfate was experimentally determined in buffers commonly employed in micellar electrokinetic chromatography. The alteration of retention factors of solutes caused by the influence of urea addition on the critical micelle concentration of sodium dodecyl sulfate was calculated under the assumption of constant distribution coefficients and compared to experimentally obtained values. It was demonstrated that the addition of urea or of D-glucose does not alter the phase ratio substantially.     

Separation of anabolic steroids by micellar electrokinetic capillary chromatography

Summary The separation of seven analogous anabolic steroids was studied by micellar electrokinetic capillary chromatography (MECC). The retention order was found to be dependent on polarity. All of these steroids were well separated by the addition of organic modifiers to the separation buffer. Of the organic modifiers tested, 1-propanol gave the best separation, better than methanol or acetonitrile.     

The separation of herbicides by micellar electrokinetic capillary chromatography

Summary A method for the separation of a number of herbicides consisting of chlorophenoxy acids by micellar electrokinetic capillary chromatography (MECC) was developed. Sodium dodecyl sulphate (SDS), Brij 35, cetyltrimethylammonium bromide (CTAB) and methanol were introduced into the buffers to investigate their effects on the separation of the herbicides. SDS combined with Brij 35 as the micellar agent was found to provide the best overall separation of these components.     

Determination of heterocyclic compounds by micellar electrokinetic capillary chromatography

Micellar electrokinetic capillary chromatography (MECC) based on sodium cholate (NaCh) and sodium dodecyl sulphate (SDS) was developed for the determination of aromatic amino acids and heterocyclic legume constituents. The influence of temperature, voltage, micellar system, pH, zwitterion and modifier concentrations in the buffer on migration times, peak areas, resolution and number of theoretical plates was investigated. This MECC method makes possible the sensitive determination of the individual compounds with detection limits in the picomole range. Up to 300 000 theoretical plates per metre of capillary were obtained together with satisfactory linearity and repeatability of the NaCh method. The applicability of MECC to samples prepared from plant material, following a fast and simple technique of isolation, purification and group separation, is illustrated by selected examples.     

Determination of plasma heparin by micellar electrokinetic capillary chromatography

The micellar electrokinetic capillary chromatography (MECC) method is reported for the separation of heparin, and for the possibility of direct determination of free heparin in plasma. The conditions for MECC were: pH 8.5, 25 mM sodium dodecyl sulfate (SDS), 25 mM borate buffer, with a 30 cmx50 mum ID fused-silica capillary. The sample was detected with a UV-detector at 270 nm with heparin as external standard. The recovery rate was 95.6-98.7%. This method was linear in the range 80-7000 U l(-1). The within-run and between-run relative standard deviations were lower than 3.1 and 4.5%, respectively. It is suggested that this MECC method may be used to determine blood samples containing high levels of heparin.     

Pharmaceutical analysis using micellar electrokinetic capillary chromatography

The potential utility in pharmaceutical analysis of a capillary electrokinetic separation technique that employs a micellar "pseudo-stationary phase" is discussed and illustrated. Chromatograms of separations of vitamin metabolites and derivatized amino acids are presented to illustrate the high efficiency of the technique and the ability to simultaneously separate the charged and neutral components of pharmaceutical samples. The analytical characteristics of the technique and the importance of optimizing experimental parameters, such as surfactant concentration and capillary column diameter, are discussed and demonstrated with the aid of chromatograms.     

Analysis of intracellular reactive oxygen species by micellar electrokinetic capillary chromatography with laser-induced-fluorescence detector

Reactive Oxygen Species (ROS) are an important part of the normal cell growth cycle and play essential roles in many biological functions. Many techniques have been developed to detect and measure the amount of ROS present in cells. These techniques include spectrophotometry, high performance liquid chromatography (HPLC), capillary electrophoresis with laser-induced-fluorescence detector (CE-LIF) and capillary electrophoresis-on-a-chip with LIF. As ROS has a short half-life outside of the cell, various fluorescent probes, such as dihydrorhodamine 123 (DHR 123), that are membrane permeable have been used in the detection of intracellular ROS. In this paper, micellar electrokinetic capillary chromatography (MEKC) was coupled with LIF detector. Fluorescent probe, 3′-(p-aminophenyl)-fluorescein (APF), was used to detect specific ROS in Chinese Hamster Ovary (CHO) suspension cells as well as attached mouse bone marrow-derived dendritic cells (BMDCs). Separation buffer composition was optimized at a concentration of 25?mM tetraborate buffer with 50?mM sodium dodecyl sulfate at pH 9.3 and lysis of the cells was done successfully with a buffer of 70% ethanol and 0.1mM sodium dodecyl sulfate using a cell amount of 1?×?10⁷. ROS in cells was successfully analyzed by MEKC-LIF method developed, with acceptable RSD for time at 1.54% and area at 2.81%.     

Analysis of B6 vitamers by micellar electrokinetic capillary chromatography with laser-excited fluorescence detection

Micellar electrokinetic capillary chromatography (MECC) involves the application of a high voltage (10 to 40 kV) across a capillary column (25 to 75 microns i.d.) that is filled with a solution containing micelles. The mobile phase in this work consists of sodium dodecyl sulfate in an aqueous phosphate/borate buffer system. Pyridoxine (vitamin B6) and five of its metabolites are separated, with efficiencies as high as 60,000 theoretical plates/meter. Pyridoxic acid, a metabolite of B6, is separated and quantitated in human urine using laser-excited fluorescence detection. Limits of detection are less than a picogram injected.     

Adjusting selectivity in micellar electrokinetic capillary chromatography with 1,2-hexanediol

In this report, we introduce a new micelle modifier useful to alter selectivity in micellar electrokinetic capillary chromatography (MECC). 1,2-Hexanediol acts as a class I organic modifier in that its effects are on the sodium dodecyl sulfate (SDS) micellar rather than the surrounding aqueous phase. This characteristic allows 1,2-hexanediol to improve resolution when applied at concentrations as low as 20 mM (0.25% v/v) by altering the selectivity observed with SDS alone. The effects of 1,2-hexanediol on the critical micelle concentration of SDS, electroosmotic flow, electrophoretic mobility of the SDS micelle, and reproducibility are presented. 1,2-Hexanediol had little impact on the migration time window at concentrations below 100 mM. Changes in selectivity induced by 1,2-hexanediol for a large set of model compounds are presented. Analytes capable of forming hydrogen bonds tend to decrease their interactions with the micellar phase while nonhydrogen bonding analytes increase their interactions. The usefulness of 1,2-hexanediol was demonstrated by examining its effects on the separation of dansylated amino acids. Eighteen of twenty amino acids could be separated with a resolution greater than 1.6 within 1600 s using a combination of 1,2-hexanediol and isopropanol.     

Determination of piribedil in pharmaceutical formulations by micellar electrokinetic capillary chromatography

A fast and simple micellar electrokinetic capillary chromatographic method was developed for the analysis of piribedil in pharmaceutical formulations. The effects of buffer concentration, buffer pH, sodium dodecyl sulphate (SDS) concentration, organic modifier, applied voltage and injection time were investigated. Optimum results were obtained with a 50 mM borate buffer at pH 8.0 containing 50 mM SDS by using a fused silica capillary (50 m internal diameter, 72 cm effective length). The sample was injected hydrodynamically for 4 s at 50 mbar pressure and the applied voltage was +30 kV. The detection wavelength was set at 205 nm. Diflunisal was used as an internal standard. The analysis was performed at 25 °C and the total run time was 14 min. The method was suitably validated with respect to linearity range, limit of detection and quantification, precision, accuracy, specificity and robustness. The linear calibration range was 5–100 g mL^–1 and the limit of detection was determined as 1 g mL^–1. The method developed was successfully applied to the determination of piribedil in pharmaceutical formulations. The results were compared with a spectrophotometric method reported in the literature and no significant difference was found statistically.     

Determination of pesticides in drinking water by micellar electrokinetic capillary chromatography

A new analytical procedure using a two-step sample preconcentration (solid-phase extraction (SPE) and field-amplified sample stacking) prior to separation by micellar electrokinetic capillary chromatography was developed for the determination of 14 pesticides such as aldicarb, carbofuran, isoproturon, chlorotoluron, metolachlor, mecoprop, dichlorprop, MCPA, 2,4-D, methoxychlor, TDE, DDT, dieldrin, and DDE in drinking water. Good recoveries of pesticides were obtained using SPE with sample pH adjusted to 2-3. Field-amplified sample stacking was found to give enrichment factors up to 30-fold preconcentration of various pesticides under reversed polarity at -2 kV for 50 s. The optimized background electrolyte (BGE) consisted of 50 mM sodium dodecyl sulfate (SDS), 10 mM borate buffer, 15 mM beta-cyclodextrin (beta-CD), and 22% acetonitrile at pH 9.6, running was under 25 kV and detection at 202 nm. Good linearity was obtained for all pesticides with detection limits down to 0.04-0.46 ng/mL and a working range of 0.1-40 ng/mL. The repeatabilities of migration time and peak area were satisfactory with relative standard deviations (RSDs) between 0.66 and 13.6% and 4.1 and 28%, respectively. All pesticides except dieldrin were found to be detected at concentrations at least tenfold lower than the World Health Organization (WHO) guideline values. The analytical procedure developed offers an economic method for fast screening of multiple pesticide residues in drinking water for health protection. It had been applied to determine carbofuran and MCPA in agricultural run-off water samples, giving satisfactory repeatabilities of 10 and 12%, respectively, with n=5 for the determination of pesticides in contaminated water samples.